Figure 15 shows that the 25 bit extended prefix assigns 9 bits to the
subnet number field. Since 29 = 512, nine bits allow the definition of
512 subnets. Depending on the organization's requirements, the net 
work administrator could have elected to assign additional bits to the
host number field (allowing more hosts on each subnet) and reduce the
number of bits in the subnet number field (decreasing the total number
of subnets that can be defined). 
Although this example creates a rather large number of subnets, it illus 
trates what happens to the dotted  decimal representation of a subnet
address when the subnet number bits extend across an octet boundary.
Note that the same type of confusion can occur when the host number
bits extend across an octet boundary. 
Defining Each of the Subnet Numbers
The 512 subnets will be numbered 0 through 511. The 9 bit binary rep 
resentation of the decimal values 0 through 511 are: 0 (0000000002 ), 1
(0000000012 ), 2 (0000000102 ), 3 (0000000112 ), ..., 511 (1111111112 ).
To define Subnet #3, the network administrator places the binary rep 
resentation of 3 (0000000112 ) into the 9 bits of the subnet number
field. The 512 subnet numbers for this example are listed in the follow 
ing sample code. The underlined portion of each address identifies the
extended network prefix, while the bold digits identify the 9 bits repre 
senting the subnet number field: 
Base Net: 10001100.00011001 .00000000.00000000 = 140.25.0.0/16
Subnet #0: 10001100.00011001.00000000.0 0000000 = 140.25.0.0/25
Subnet #1: 10001100.00011001.00000000.1 0000000 = 140.25.0.128/25
Subnet #2: 10001100.00011001.00000001.0 0000000 = 140.25.1.0/25
Subnet #3: 10001100.00011001.00000001.1 0000000 = 140.25.1.128/25
Subnet #4: 10001100.00011001.00000010.0 0000000 = 140.25.2.0/25
Subnet #5: 10001100.00011001.00000010.1 0000000 = 140.25.2.128/25
Subnet #6: 10001100.00011001.00000011.0 0000000 = 140.25.3.0/25
Subnet #7: 10001100.00011001.00000011.1 0000000 = 140.25.3.128/25
Subnet #8: 10001100.00011001.00000100.0 0000000 = 140.25.4.0/25
Subnet #9: 10001100.00011001.00000100.1 0000000 = 140.25.4.128/25
.
.
Subnet #510: 10001100.00011001.11111111.0 0000000 = 140.25.255.0/25
Subnet #511: 10001100.00011001.11111111.1 0000000 = 140.25.255.128/25 
Note that the sequential subnet numbers are not sequential when
expressed in dotted decimal notation. This can be confusing to people
who expect dotted decimal notation to make IP addressing easier. In
this example, the dotted decimal notation obscures the subnet number 
ing scheme. 
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